Figure 11.

a) Catalysis of a crossed‐aldol reaction involving two aldehydes by two pyrrolidine moieties cooperatively working together. The catalytic groups are positioned together in space through the folding of β‐ or α/β‐peptides. Adapted with permission.^{[ 202 ]} Copyright 2020, The American Chemical Society. b) The catalyzed cross‐aldol reaction of a bisaldehyde moiety results in the formation of a macrocycle due to the decreased entropic cost. Reproduced with permission.^{[ 205 ]} Copyright 2019, AAAS.